1. Field of the Invention
The subject matter of the present invention relates to a method for metallurgically bonding a cast-in-place cylinder liner to a cast cylinder block of an internal combustion engine.
2. Description of the Related Prior Art
It is known to the art to form light weight aluminum cylinder blocks having cast-in-place cylinder liners. These liners are typically made of materials exhibiting wear properties superior to the aluminum cylinder block metal.
One known method for securing the cast-in-place liners within the block is to create a mechanical bond between the liners and block. An example of such a process is disclosed in U.S. Pat. Nos. 1,528,947 to Preston, granted Mar. 10, 1925 and 3,069,209 to Bauer, granted Dec. 18, 1962. Mechanically interlocked cylinder liners, however, tend to loosen over time due to the repeated cycling of temperature experienced during normal operation. Liner retention is, of course, important to the performance of an engine.
One solution to the above problem is to form a metallurgical bond between the cylinder liners and cylinder block. The metallurgical bond unites the liners and the cylinder block with a chemical bond. It is common with this type of process to first coat the outer surface of the cylinder liners with a low melting point metal material, such as zinc. The coated liners are then placed within a cylinder block casting mold after which molten cylinder block metal is cast into the mold and about the coated liners. The heat of the molten metal causes the coating material on the liners to melt in preparation for alloying with the cylinder block metal. Examples of such processes are disclosed in the U.S. Pat. No. 3,276,082 to Thomas, granted Oct. 4, 1966. Although this metallurgical bonding process should, in theory, work, it has been found that an unacceptably limited amount of metallurgical bonding results. It is believed the primary reason for such poor results is attributable to the presence of oxidation on the surface of the coating. The oxidation acts as a barrier to metallurgical bonding by inhibiting the molten cylinder block metal from mixing with the coating material beneath the oxidation.